This is an indicator or how a person has set their Gender in their profile. This is a user controlled field, and does not necessarily reflect reality.

If this Gender field is set to Female, the red heart is shown. If it is not set, or set to a different value, no heart is shown.

To change your profile settings:

go to http://forum.myredbook.com/board
click LOGIN link and login (if you are not already logged in)
click USER MENU link
click EDIT YOUR PROFILE
set Gender = Female

While you are there, you can EDIT YOUR PREFERENCE.
As a reminder, your profile also controls whether you want to accept rb-mail (Use private messaging system?)

Your email address is always disabled regardless of the setting.